1. Field of the Invention
This invention relates to semiconductor integrated circuits and, more particularly, to metal fill structures and metallization layers within semiconductor integrated circuits.
2. Description of the Related Art
Integrated Circuits (ICs) are manufactured using complex processes including a variety of specific processing steps. Typically, the solid-state devices that make up an IC are formed on the surface (or substrate) of a semiconducting material such as silicon, for example. Although silicon has been the most widely used semiconducting material, other materials such as Gallium-Arsenide (GaAs) and Silicon-Germanium (SiGe) have also become popular for certain applications including analog and specialty integrated circuits. Once the devices have been formed, the individual components are interconnected. The devices are typically interconnected by metal lines or wires made from aluminum, copper, tungsten or some other conductive material. The metal lines are typically manufactured by depositing layers of metal over the entire surface of the wafer and then precisely etching away areas other than those defining the metal lines. Due to the high density of devices, most modern ICs include multiple metal layers that may be separated by an interlayer dielectric (ILD).
Analog and mixed signal ICs may rely on high quality passive devices such as capacitors and inductors for proper circuit operation. Mixed signal ICs may include both analog and digital circuits that are manufactured on the same semiconducting substrate. As process technologies have improved, it has become more common to build passive devices such as inductors onto the die as part of the IC. A typical IC inductor may have one or more loops (or coils) of conductive material formed onto one or more layers of the integrated circuit.
In conventional ICs, the die areas adjacent (i.e., inside the loop and in close proximity to the exterior part of the inductor loop) to the inductor loop are typically left void of metal and thus filled with dielectric material. In some cases, these unused areas may present manufacturing issues. For example, it is sometimes desirable in IC designs to maintain consistent metal density and uniformity for manufacturability reasons and to ensure good planarization. Typically the goal is to increase the metal density to above 20% but below about 70% or 80% and in a uniform way. Fill programs are commonly used to add metal dummy fill structures wherever it is considered necessary. However, in some designs such as analog designs the dummy metal fill structures may not be desirable since they may detrimentally affect circuit performance. More particularly, placing some types of metal structures such as the dummy fill structures, within the loop or in close proximity to the exterior part of the inductor loop may adversely affect the electrical characteristics of the inductor.
It would accordingly be desirable to provide an integrated circuit structure that may provide desired metal density while reducing some of the adverse effects associated with conventional fill metal in close proximity to inductors.